Reading your weeds—what's your soil telling you?

So, it’s mid March, which means that the summer growing season is a few short weeks away, and many springtime plants will be popping up soon. Although you might already be starting seeds for this year’s garden, it’s important to survey your growing area long before you pop any tomatoes into the ground. Some of the plants you’d like to grow this year might not be ideal for the soil you have, and reading the “weeds” that spring up in your space can give you a solid idea of what your soil is like, and what it might need, before investing time and energy into a garden only to have it fall short of your hopes and expectations.

I put “weeds” in quotation marks here because so many plants that are labeled as such—i.e. unvalued, undesired, and troublesome—are actually spectacular plants in their own right: some are edible, some are medicinal, but each and every one serves a purpose. Some, like clover, deposit nitrogen into soil that desperately needs it, while yarrow provides potassium to hungry earth. If you pay attention to the weeds that pop up in your garden, you can probably get a solid idea of what your soil is composed of, and you can then determine whether you’d like to try amending it to suit the plants you’d like in there, or to choose plants that are better suited to the soil you have.

Dandelions

If these (rather delicious) “pests” are plentiful in your garden space, chances are that your soil is fairly acidic, but also well aerated: dandelions have a tap root, which helps to break up soil and allow water and nutrients to flow into it. Pulling these out by the root will allow even more goodness to seep into the soil, and you can use the pulled plants for salads, fritters, tea, or even wine. If none of those appeal to you, you can compost them instead. Should you decide that you really don’t want any dandelions in your garden at all, be diligent about popping their flowers off when they appear: this will stop seeds from developing and scattering around your yard.

Should you decide to attempt to make your soil more alkaline, you can amend it with limestone (calcium carbonate), hardwood ash, bone meal, or crushed oyster shells.

Wood Sorrel

This little plant has clover-like leaves and yellow flowers, and springs up wherever the soil is both acidic, and highly comprised of clay.

It’s edible as well, giving a sour, lemony note to salads and soups, but take care not to eat an entire bucket of the stuff, as the oxalic acid within the leaves can cause kidney issues when consumed in high doses.

Mullein

Should you find a significant amount of mullein around, chances are that your soil is extremely dry; chronically dry, even. Since you’ll often find it near beaches, it’s likely that your soil also has a fair amount of sand in it. Should you decide not to harvest the leaves for medicinal purposes, you can use them as a mulch once autumn rolls around again.

Clover

Both red and white clover deposit nitrogen in the soil, and their appearance in your garden can signify either very fertile soil, or poor soil that’s on its way to becoming more fertile: check out the other plants growing around it, as they’ll help you determine clover’s function. This is a great cover crop to sow in an area that you can leave fallow for a year—working it into the soil as a mulch will add significant nutrients to it for the following season’s crop.

Yarrow

Like clover, yarrow can show up in different soil types, but it tends to thrive in dry conditions. If yarrow is suddenly springing up in your yard, it may be a sign of deteriorating soil quality, especially if it’s showing up with both dandelion, clover, mullein, or plantain.

Plantain

This stuff thrives in soil that’s low in nutrients and fertility, but fortunately it has plenty of good stuff tucked into its own leaves. If you don’t harvest the young leaves as an edible green, you can add them to your compost and use the broken-down matter as an amendment. If you have a lot of plantain growing in your area, you might wish to look into its many medicinal uses as well.

Crabgrass

If this stuff is showing up around your garden, you have some pretty moist (and highly fertile) soil to contend with. It thrives in poorly-drained soil, and will often show up in conjunction with various mosses.

If you can’t easily identify the plants in your garden and are uncertain about the soil therein, it’s not a bad idea to have a soil test done. You can either arrange one through your local nursery, or by picking up a home pH test from any home improvement or garden center. You could even go the super-low-tech route by using the baking soda/vinegar test, but that won’t give you an exact pH reading; it’ll just give you the basic awareness of whether your soil is seriously on the acidic or alkaline side.

When it comes to spreading mulch or other soil amendments, it’s usually best to add them in as soon as the earth is warm and moist, so a week or so after the last frost warning in your area. Choose a warm day after there has been a solid rain so that the soil is damp (and thus will both absorb and hold nutrients more easily), and rake your amendment through the top soil. If you plan to amend in autumn instead, do so before the first frost, be sure to add a few inches of the compost of your choice, and then let it all break down over the winter. This can actually be a better way of amending the soil, as the nutrients will have all winter to seep into the earth to replenish it.

Knowing all you can about both the soil and local flora can only be of benefit as you cultivate the garden of your dreams: you’ll be better educated about what will thrive in the space you have if you really know what you’re working with.